In addition to completing projects on MYO15 involving its function in stereocilia development, we continue to pursue studies of mouse models of human deafness genes that have been identified in the LMG. At least two of the three major isoforms of TRIOBP (TRIOBP-4 and TRIOBP-5) are necessary for normal hair cell stereocilia rootlet formation and the maintenance of stereocilia rootlets in the adult organ of Corti. Rootlets provide bundle stiffness necessary for the detection of sound. The function of TRIOBP-1, if any, in the auditory system has not been examined. TRIOBP-1 is necessary for embryonic development. A body-wide ablation of expression of TRIOBP-1 is lethal during development. To understand the function of TRIOBP-1 in the auditory system we have developed a floxed allele of a unique exon of the TRIOBP-1 isoform and will delete TRIOBP-1 expression just in the auditory system using appropriate cre-expressors. Similar strategies will be used to study the function of several other genes necessary for hearing.